Ferdinand Mount describes himself as having 'a languid upper-class voice and a semi-dormant baronetcy', whatever that is. Aha! this is the fun of writing about class: you can bitch about other people and simultaneously bask in an assumed sense of solidarity.

Creditably, Mount mostly avoids this trap of bad manners in his new polemic, with which almost no one will entirely agree. Most readers, though, are probably are going to have an 'Ah, yes!' moment, a sense that at least here, he's put his finger on something.

It takes a bit of time to get to his central argument, because he first wants to demolish the notion that Britain has become a classless society. The familiar stuff about inequality is persuasive enough, but, confusingly, fails to draw a fault line. For the entire book, whenever Mount talked of his two classes, which he calls the Uppers and Downers, I couldn't tell exactly where one was supposed to end and the other begin.

Are the Downers the underclass? The former working classes? Anyone whose children go to a comprehensive? He slithers away from definitions, which, of course, conveniently gives him a lot of leeway. Never mind: when we do get there, his argument is interesting. Mount believes that in the years (roughly) between 1800 and 1940 the British lower classes built a remarkable civilisation and then the upper classes destroyed it.

This civilisation, steadfast and idealistic, was formed by and expressed through the dissenting churches, the movement for working-class self-improvement (mechanics' institutes and the like) and the growth of a powerful morality, in which patriotism played a sustaining part.

Sometimes, he overdoes it: he was evidently never in danger of an education at a secondary modern himself, and his celebration of them as splendid places doesn't stack up for those of us who were. And he signally fails to explain why exactly the middle classes should have been so afraid of their industrious, peaceable, self-improving compatriots as to deride and erode their institutions.

He makes a good case, though, that that's what happened. He's particularly good on the ridiculing of nonconformism. (EP Thompson described Methodism as 'a ritualised form of psychic masturbation', rage and disdain seeping out of his words). Poorer people were systematically infantilised (you don't get domestic violence social work specialists knocking on doors in South Kensington, even though rich men beat their wives) and suffered 'deprivation of respect'.

He suggests that the reason that Britons, pretty much alone, look back with such nostalgia to the war is that it was the high point (and, as it turned out, the end point) of the feeling that everyone was in this together and that all had some role to play.

Now, instead, a group of people in society has been thrown back on to personal relations as the sole means of self-expression and self-actualisation. A terrible burden is placed on intimacy, from which there is no escape. Unbuttressed by other worldly achievements, relationships are not robust enough to withstand the pressure. A lot of this is straightforward Tory stuff: anti-state; in favour of little platoons. Mount's recommendations, though, seem to be anything but: 'Only a wholehearted, even reckless opening up of genuine power to the bottom classes is likely to improve their self-esteem,' he writes.

He wants to give schools and hospitals back to their customers (not far from what some parts of the government are thinking) and suggests carving up the countryside into smallholdings, on which people would be allowed to erect shops, shacks, garages and caravans, creating an allotment landscape of untidy activity.

By the end, I still didn't know who exactly the Downers were or understand the wellsprings of the Uppers' destructiveness. Mount is almost entirely silent on the subject of ethnicity, which has had a profound impact on class in Britain since the 1950s. Asians, for instance, seem to buck the trend of reduced social mobility since the 1970s.

Nor does he talk about the most significant development of the period: the absorption of much of the former working class into the middle class. This change in self-identification, which is the direct result of the postwar settlement he so despises, has had profound consequences for those 'left behind'.

So I don't think it adds up. But it's full of insights and fires off ideas like a sparkler.